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Question
How would you separate the mixtures given in Table 5.3? Mention the reason for choosing your method. If a mixture cannot be separated, explain why.
| Mixture | Method of separation | Reason for selection |
|---|---|---|
| Mud from muddy water | — | — |
| Plasma from other components in the blood sample | — | — |
| Naphthalene and sand | — | — |
| Chalk powder and common salt | — | — |
| Common salt and water | — | — |
| Oil from water | — | — |
| Pigments of the flower | — | — |
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Answer
Each mixture is matched to the one property in which its components differ.
Explanation
| Mixture | Method | Reason |
|---|---|---|
| Mud from muddy water | Coagulation with alum, then sedimentation, then decantation or filtration | The mud particles are fine and do not dissolve; filtration alone leaves the water cloudy, so they must first be clumped together |
| Plasma from other components in the blood sample | Centrifugation | The components differ in density; on fast spinning the heavy cells go down and the light plasma stays above |
| Naphthalene and sand | Sublimation | Naphthalene turns straight into vapour on heating; sand does not sublime |
| Chalk powder and common salt | Dissolve in water, filter, then evaporate or crystallise the filtrate | Salt dissolves and chalk does not, so chalk becomes the residue and salt goes into the filtrate |
| Common salt and water | Evaporation if only the salt is wanted; distillation if both are wanted | The salt is dissolved and the boiling points differ enormously |
| Oil from water | Separating funnel | The two are immiscible and their densities differ |
| Pigments of the flower | Paper chromatography | Different pigments hold on to the solvent and the paper differently, so they climb at different speeds |
Find the property that differs, and the method chooses itself.
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